The present invention relates to an improvement in electron guns for cathode ray tubes. The improved gun is primarily intended for use in a color tube having a line type color phosphor screen, with or without light absorbing guard bands between the color phosphor lines, and a mask having elongated apertures or slits. However, the gun improvement could be used in the well known dot-type color tube having a screen of substantially circular color phosphor dots and a mask with substantially circular apertures. The invention may also be applied to other types of cathode-ray tubes such as penetration or focus-grill tubes.
An in-line electron gun is one designed to generate or initiate at least two, and preferably three, electron beams in a common plane, for example, by at least two cathodes, and direct those beams along convergent paths in that plane to a point or small area of convergence near the tube screen.
There has been a general trend toward color picture tubes with greater deflection angles in order to provide shorter tubes. In the transition to a wider deflection tube, e.g., 90.degree. deflection to 110.degree. deflection, it has been found that the electron beam becomes increasingly more distorted as it is scanned toward the outer portions of the screen. Such distortions may be due, at least in part, to variations in the deflection field formed by a yoke mounted on the tube. It is the purpose of the present invention to at least partially compensate for these distortions.
Although the present invention may be applied to several different types of tubes, it is hereinafter described as an improvement on a tube having an in line gun, such as disclosed in U.S. Pat. No. 3,772,554 issued to Hughes on Nov. 13, 1973. For the purpose of gun construction and operation, U.S. Pat. No. 3,722,554 is hereby incorporated by reference. Additionally, for the purpose of yoke construction and operation U.S. Pat. No. 3,721,930 issued to Barkow et al on Mar. 20, 1973 also hereby incorporated by reference as describing a representative yoke.